Interaction of components of glass-forming melts of iron and nickel with titanium, zirconium and hafnium
II. Temperature-concentration dependence  of thermodynamic mixing functions of liquid alloys

Abstract

The thermodynamic properties of liquid alloys of the glass-forming systems were described within the framework of the associated solution model (ASM) according to the information on their mixing enthalpies presented in the previous communication. The results of calculations at 1873 K show that the values and topology of excess thermodynamic mixing functions are determined by the pair interactions between the IVB-metal and the late transition metal. The minimum values of the Δ_mH, Δ_mS^ex, and Δ_mG^ex functions for each of the ternary systems are related to the limiting two-component system Ni–IVB-metal. The Gibbs energy minima of mixing Δ_mG of liquid alloys at 1873 K are inside the concentration triangle, which is due to the significant contribution of the ideal component Δ_mG^id. The results of calculations of thermodynamic mixing functions in the range of 800…1873 K point to an increase in negative deviations from ideality and increase the dominant effect on them of pairwise interactions of components with decreasing temperature. In the considered temperature range, the formation of the liquid alloys is accompanied by a significant increase in their thermodynamic stability, which determines their glass forming ability. The composition of the associated solution, which corresponds to the melts of the systems, was calculated within the framework of ASM and the short-range chemical ordering degree was estimated as the total molar fraction of associates Σx_аssoc. It is shown that the chemical ordering degree in the ternary systems melts increases with decreasing temperature. In accordance with the empirical rule, the predicted concentration interval of amorphization of Fe–Ni–Ti, Fe–Ni–Zr and Fe–Ni–Hf melts was determined as x_Me ≈ 0.18…0.76, where x_Me is the molar fraction of IVB–metal.